Golf ball

ABSTRACT

A golf ball 2 includes a main body 4 and a paint layer 6 positioned outside the main body 4. The main body 4 includes a spherical core 8, a mid layer 10 positioned outside the core 8, and a cover 12 positioned outside the mid layer 10. An indentation depth, measured when the paint layer 6 in a cross-section along a plane passing through a central point of the golf ball 2 is pressed by a force of 30 mgf in a direction perpendicular to the cross-section, is not less than 300 nm and not greater than 3000 nm. The paint layer 6 preferably has a thickness of not less than 5 μm and not greater than 50 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending U.S. application Ser. No.16/549,182, filed on Aug. 23, 2019, which is a Divisional of U.S.application Ser. No. 15/786,071, filed on Oct. 17, 2017 (now U.S. Pat.No. 10,569,139 issued on Feb. 25, 2020), which claims priority under 35U.S.C. § 119(a) to Patent Application No. 2016-232270 filed in JAPAN onNov. 30, 2016. The entire contents of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to golf balls. Specifically, the presentinvention relates to golf balls having a paint layer on the surfacethereof.

Description of the Related Art

When a golf ball is hit with a golf club, the golf ball flies withbackspin. When the rate of the backspin is high, the run of the golfball after landing is short. By using a golf ball having a high backspinrate, a golf player can cause the golf ball to stop at a target point.When the rate of sidespin is high, the golf ball tends to curve. Byusing a golf ball having a high sidespin rate, a golf player canintentionally cause the golf ball to curve. For golf players, the spinperformance of golf balls is important.

Golf players place importance on feel at impact of golf balls as well asspin performance. Golf players prefer soft feel at impact.

Most golf balls have a paint layer on the surface thereof. The roles ofthe paint layer are to enhance the appearance of golf balls and preventstaining of golf balls. Furthermore, the paint layer can also contributeto spin performance and feel at impact.

JP2011-217820 (US2011/0244989 A1) discloses a golf ball including apaint layer having a predetermined Martens hardness and a predeterminedmodulus. The golf ball has excellent spin performance in a wet state.

JP2013-126541 (US2013/0157782 A1) discloses a golf ball including apaint layer having a predetermined Young's modulus. The golf ball hasexcellent spin performance. JP2013-126542 (US2013/0157782 A1 andUS2013/0157784 A1) and JP2013-126543 (US2013/0157782 A1 andUS2013/0157783 A1) also disclose similar golf balls.

JP2014-14383 (US2013/0331205 A1) discloses a golf ball including a paintlayer having a predetermined storage modulus and a predetermined losstangent. The golf ball has excellent spin performance upon an approachshot.

JP2016-123632 (US2016/0184654 A1) discloses a golf ball including apaint layer having a predetermined elastic modulus. The golf ball hasexcellent stain resistance.

Since the paint layer is thin, it is difficult to directly measure thephysical properties of the paint layer. The Martens hardness and themodulus disclosed in JP2011-217820 (US2011/0244989 A1) are measured on aslab having the same composition as the composition of the paint layer.Therefore, the measurement results do not accurately reflect behavior ofthe paint layer in the golf ball. The spin performance of the golf balldisclosed in JP2011-217820 is not sufficient.

The Young's modulus disclosed in JP2013-126541 (US2013/0157782 A1) ismeasured on a sheet having a thickness of 2 mm. Therefore, themeasurement results do not accurately reflect behavior of the paintlayer in the golf ball. The spin performance of the golf ball disclosedin JP2013-126541 is not sufficient. The spin performance of the golfballs disclosed in JP2013-126542 (US2013/0157782 A1 and US2013/0157784A1) and JP2013-126543 (US2013/0157782 A1 and US2013/0157783 A1) is alsonot sufficient.

The storage modulus and the loss tangent disclosed in JP2014-14383(US2013/0331205 A1) are measured on a film having the same compositionas the composition of the paint layer. Therefore, the measurementresults do not accurately reflect behavior of the paint layer in thegolf ball. The spin performance of the golf ball disclosed inJP2014-14383 is not sufficient.

The elastic modulus disclosed in JP2016-123632 (US2016/0184654 A1) ismeasured with a scanning probe microscope. Therefore, the measurementresults are influenced by the physical properties of a cover under thepaint layer. The spin performance of the golf ball disclosed inJP2016-123632 is not sufficient.

An object of the present invention is to provide a golf ball havingexcellent spin performance, excellent feel at impact, and excellentstain resistance. Another object of the present invention is to providean evaluation method by which a true physical property of a paint layercan be measured.

SUMMARY OF THE INVENTION

A golf ball according to the present invention includes a main body anda paint layer positioned outside the main body. An indentation depth,measured when the paint layer in a cross-section along a plane passingthrough a central point of the golf ball is pressed in a directionperpendicular to the cross-section, is not less than 300 nm and notgreater than 3000 nm.

The golf ball according to the present invention has excellent spinperformance, excellent feel at impact, and excellent stain resistance.

Preferably, the indentation depth is not less than 400 nm and notgreater than 3000 nm.

Preferably, the paint layer has a thickness of not less than 5 μm andnot greater than 50 μm.

The main body may include a core and a cover positioned outside thecore. The paint layer is laminated on the cover. Preferably, the coverhas a Shore D hardness of not less than 20 and not greater than 50, andthe indentation depth is not less than 400 nm and not greater than 3000nm. The cover may have a Shore D hardness of not less than 50 and notgreater than 80, and the indentation depth may be not less than 300 nmand not greater than 2500 nm.

A golf ball evaluation method according to the present inventionincludes the steps of:

-   -   cutting a golf ball including a paint layer; and    -   pressing a cross-section of the paint layer exposed as a result        of the cutting and measuring an indentation depth of the paint        layer.

By the evaluation method according to the present invention, a physicalproperty of the paint layer of the golf ball can be objectivelyevaluated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway cross-sectional view of a golf ballaccording to one embodiment of the present invention; and

FIG. 2 is a partially cutaway cross-sectional view of a golf ballaccording to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention based onpreferred embodiments with appropriate reference to the drawings.

First Embodiment

A golf ball 2 shown in FIG. 1 includes a main body 4 and a paint layer 6positioned outside the main body 4. The main body 4 includes a sphericalcore 8, a mid layer 10 positioned outside the core 8, and a cover 12positioned outside the mid layer 10. The golf ball 2 has a so-calledthree-piece structure. The golf ball 2 has a plurality of dimples 14 onthe surface thereof. Of the surface of the golf ball 2, a part otherthan the dimples 14 is a land 16. The golf ball 2 may include a marklayer. The mark layer may be positioned between the cover 12 and thepaint layer 6, or may be positioned outside the paint layer 6.

The golf ball 2 preferably has a diameter of not less than 40 mm and notgreater than 45 mm. From the viewpoint of conformity to the rulesestablished by the United States Golf Association (USGA), the diameteris particularly preferably not less than 42.67 mm. In light ofsuppression of air resistance, the diameter is more preferably notgreater than 44 mm and particularly preferably not greater than 42.80mm. The golf ball 2 preferably has a weight of not less than 40 g andnot greater than 50 g. In light of attainment of great inertia, theweight is more preferably not less than 44 g and particularly preferablynot less than 45.00 g. From the viewpoint of conformity to the rulesestablished by the USGA, the weight is particularly preferably notgreater than 45.93 g.

The core 8 is formed by crosslinking a rubber composition. Examples ofthe base rubber of the rubber composition include polybutadienes,polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-dienecopolymers, and natural rubbers. Two or more rubbers may be used incombination. In light of resilience performance, polybutadienes arepreferable, and high-cis polybutadienes are particularly preferable.

The rubber composition of the core 8 includes a co-crosslinking agent.Examples of preferable co-crosslinking agents in light of resilienceperformance include zinc acrylate, magnesium acrylate, zincmethacrylate, and magnesium methacrylate. The rubber compositionpreferably includes an organic peroxide together with a co-crosslinkingagent. Examples of preferable organic peroxides include dicumylperoxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.

The rubber composition of the core 8 may include additives such as afiller, sulfur, a vulcanization accelerator, a sulfur compound, ananti-aging agent, a coloring agent, a plasticizer, and a dispersant. Therubber composition may include a carboxylic acid or a carboxylate. Therubber composition may include synthetic resin powder or crosslinkedrubber powder.

The core 8 has a diameter of preferably not less than 30.0 mm andparticularly preferably not less than 38.0 mm. The diameter of the core8 is preferably not greater than 42.0 mm and particularly preferably notgreater than 41.5 mm. The core 8 may include two or more layers. Thecore 8 may have a rib on the surface thereof. The core 8 may be hollow.

The mid layer 10 is formed from a resin composition. A preferable basepolymer of the resin composition is an ionomer resin. Examples ofpreferable ionomer resins include binary copolymers formed with anα-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms. Examples of other preferable ionomer resins include ternarycopolymers formed with: an α-olefin; an α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms; and an α,β-unsaturated carboxylate esterhaving 2 to 22 carbon atoms. For the binary copolymer and the ternarycopolymer, preferable α-olefins are ethylene and propylene, whilepreferable α,β-unsaturated carboxylic acids are acrylic acid andmethacrylic acid. In the binary copolymer and the ternary copolymer,some of the carboxyl groups are neutralized with metal ions. Examples ofmetal ions for use in neutralization include sodium ion, potassium ion,lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, andneodymium ion.

Instead of an ionomer resin or together with an ionomer resin, the resincomposition of the mid layer 10 may include another polymer. Examples ofthe other polymer include polystyrenes, polyamides, polyesters,polyolefins, and polyurethanes. The resin composition may include two ormore polymers.

The resin composition of the mid layer 10 may include a coloring agentsuch as titanium dioxide, a filler such as barium sulfate, a dispersant,an antioxidant, an ultraviolet absorber, a light stabilizer, afluorescent material, a fluorescent brightener, and the like. For thepurpose of adjusting specific gravity, the resin composition may includepowder of a metal with a high specific gravity such as tungsten,molybdenum, and the like.

The mid layer 10 has a Shore D hardness of preferably not less than 40and particularly preferably not less than 50. The Shore D hardness ofthe mid layer 10 is preferably not greater than 80 and particularlypreferably not greater than 70. The mid layer 10 has a thickness ofpreferably not less than 0.2 mm and particularly preferably not lessthan 0.3 mm. The thickness of the mid layer 10 is preferably not greaterthan 2.5 mm and particularly preferably not greater than 2.2 mm. The midlayer 10 has a specific gravity of preferably not less than 0.90 andparticularly preferably not less than 0.95. The specific gravity of themid layer 10 is preferably not greater than 1.10 and particularlypreferably not greater than 1.05. The mid layer 10 may include two ormore layers.

The cover 12 is formed from a resin composition. A preferable basepolymer of the resin composition is a polyurethane. The resincomposition may include a thermoplastic polyurethane or may include athermosetting polyurethane. In light of productivity, the thermoplasticpolyurethane is preferable. The thermoplastic polyurethane includes apolyurethane component as a hard segment, and a polyester component or apolyether component as a soft segment. The cover 12 the base material ofwhich is the polyurethane can contribute to the spin performance of thegolf ball 2. Furthermore, the cover 12 can also contribute to the feelat impact of the golf ball 2.

The polyurethane has a urethane bond within the molecule. The urethanebond can be formed by reacting a polyol with a polyisocyanate.

The polyol, which is a material for the urethane bond, has a pluralityof hydroxyl groups. Low-molecular-weight polyols andhigh-molecular-weight polyols can be used.

Examples of an isocyanate for the polyurethane component includealicyclic diisocyanates, aromatic diisocyanates, and aliphaticdiisocyanates. Alicyclic diisocyanates are particularly preferable.Since an alicyclic diisocyanate does not have any double bond in themain chain, the alicyclic diisocyanate suppresses yellowing of the cover12. Examples of alicyclic diisocyanates include 4,4′-dicyclohexylmethanediisocyanate (H₁₂MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI),isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate(CHDI). In light of versatility and processability, H₁₂MDI ispreferable.

Instead of a polyurethane, the resin composition of the cover 12 mayinclude another polymer. Examples of the other polymer include ionomerresins, polystyrenes, polyamides, polyesters, and polyolefins. The resincomposition may include two or more polymers.

The resin composition of the cover 12 may include a coloring agent suchas titanium dioxide, a filler such as barium sulfate, a dispersant, anantioxidant, an ultraviolet absorber, a light stabilizer, a fluorescentmaterial, a fluorescent brightener, and the like.

The cover 12 preferably has a hardness Hc of not less than 20 and notgreater than 50. The cover 12 having a hardness Hc of not less than 20has excellent durability. From this viewpoint, the hardness Hc is morepreferably not less than 22 and particularly preferably not less than24. The golf ball 2 including the cover 12 having a hardness Hc of notgreater than 50 has excellent spin performance. From this viewpoint, thehardness Hc is more preferably not greater than 48 and particularlypreferably not greater than 46.

The hardness of the cover 12 (or the mid layer 10) is measured accordingto the standards of “ASTM-D 2240-68”. The hardness is measured with aShore D type hardness scale mounted to an automated hardness meter(trade name “digi test II” manufactured by Heinrich BareissPrüfgerätebau GmbH). For the measurement, a sheet that is formed by hotpress, is formed from the same material as that of the cover 12 (or themid layer 10), and has a thickness of about 2 mm is used. Prior to themeasurement, a sheet is kept at 23° C. for two weeks. At themeasurement, three sheets are stacked.

In light of spin performance, the cover 12 has a thickness of preferablynot less than 0.1 mm, more preferably not less than 0.3 mm, andparticularly preferably not less than 0.4 mm. In light of flightperformance of the golf ball 2, this thickness is preferably not greaterthan 2.0 mm, more preferably not greater than 1.5 mm, and particularlypreferably not greater than 1.0 mm. The thickness is measured at aposition immediately below the land 16.

The cover 12 may include two or more layers.

The golf ball 2 may include a reinforcing layer between the mid layer 10and the cover 12. The reinforcing layer firmly adheres to the mid layer10 and also to the cover 12. The reinforcing layer suppresses separationof the cover 12 from the mid layer 10. The reinforcing layer is formedfrom a polymer composition. Examples of the base polymer of thereinforcing layer include two-component curing type epoxy resins andtwo-component curing type urethane resins.

The paint layer 6 is laminated on the cover 12. The paint layer 6 isformed from a resin composition. Examples of the base material of theresin composition include polyurethanes, epoxy resins, acrylic resins,polyvinyl acetate resins, and polyesters. Particularly preferable baseresins are polyurethanes. Polyurethanes can contribute to the spinperformance of the golf ball 2.

Typically, the paint layer 6 is formed from a polyurethane paint. Thepaint contains a polyol composition and a polyisocyanate composition. Inthe paint, a polyol is a base material, and a polyisocyanate is a curingagent.

The polyol composition contains a polyol compound. The polyol compoundhas two or more hydroxyl groups within the molecule thereof. The polyolcompound may have a hydroxyl group at an end of the molecule thereof, ormay have a hydroxyl group at the portion of the molecule other than theends thereof. The polyol composition may contain two or more polyolcompounds.

The polyol compound having a hydroxyl group at an end of the moleculethereof includes a low-molecular-weight polyol and ahigh-molecular-weight polyol.

Examples of the low-molecular-weight polyol include: diols such asethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol,1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; and triols such asglycerin, trimethylol propane, and hexanetriol.

Examples of the high-molecular-weight polyol include: polyether polyols,polyester polyols, polycaprolactone polyols, polycarbonate polyols,urethane polyols, and acrylic polyols. Examples of polyether polyolsinclude polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolyoxytetramethylene glycol (PTMG). Examples of polyester polyolsinclude polyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PHMA). Examples of polycaprolactone polyolsinclude poly-ε-caprolactone (PCL). Examples of polycarbonate polyolsinclude polyhexamethylene carbonate.

From the viewpoint that the curing time of the paint is short, apreferable polyol compound is a urethane polyol. The urethane polyol hastwo or more urethane bonds and two or more hydroxyl groups. The urethanepolyol can be obtained by causing a reaction of a polyol component and apolyisocyanate component under a condition that the hydroxyl groups ofthe polyol component are excessive with respect to the isocyanate groupsof the polyisocyanate component.

Examples of the polyol component, which is a starting material of theurethane polyol, include polyether diols, polyester diols,polycaprolactone diols, and polycarbonate diols. A preferable polyolcomponent is a polyether diol. Examples of the polyether diol includepolyoxyethylene glycol, polyoxypropylene glycol, andpolyoxytetramethylene glycol. A preferable polyether diol ispolyoxytetramethylene glycol.

The polyether diol preferably has a number average molecular weight ofnot less than 550. The polyether diol having a number average molecularweight of not less than 550 can contribute to spin performance. Fromthis viewpoint, this molecular weight is more preferably not less than600 and particularly preferably not less than 630. The molecular weightis preferably not greater than 3000. The polyether diol having amolecular weight of not greater than 3000 can contribute to the stainresistance of the paint layer 6. From this viewpoint, the molecularweight is more preferably not greater than 2500 and particularlypreferably not greater than 2000. The number average molecular weight ofthe polyol component is measured by gel permeation chromatography (GPC).The measurement conditions are as follows.

Reference material: polystyrene

Eluant: tetrahydrofuran

Column: organic solvent GPC column (“Shodex KF Series” manufactured byShowa Denko K.K.)

The content of the polyether diol in the urethane polyol is preferablynot less than 60% by weight. The urethane polyol the content of which isnot less than 60% by weight can contribute to spin performance. Fromthis viewpoint, this content is more preferably not less than 62% byweight and particularly preferably not less than 65% by weight.

A low-molecular-weight polyol can be used as the polyol component, whichis the starting material of the urethane polyol. Examples of thelow-molecular-weight polyol include: diols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol,neopentyl glycol, and 1,6-hexanediol; and triols such as glycerin,trimethylol propane, and hexanetriol. Two or more low-molecular-weightpolyols may be used as the starting material.

The polyisocyanate component, which is a starting material of theurethane polyol, has two or more isocyanate groups. Examples of thepolyisocyanate component include: aromatic polyisocyanates such as2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture (TDI) of2,4-toluene diisocyanate and 2,6-toluene diisocyanate,4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate(XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylenediisocyanate (PPDI); alicyclic polyisocyanates such as4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophoronediisocyanate (IPDI), and norbornene diisocyanate (NBDI); and aliphaticdiisocyanates. As the starting material, two or more polyisocyanates maybe used.

The urethane polyol preferably has a weight average molecular weight ofnot less than 4000. The urethane polyol having a weight averagemolecular weight of not less than 4000 can contribute to spinperformance. From this viewpoint, the molecular weight is morepreferably not less than 4300 and particularly preferably not less than4500. The molecular weight is preferably not greater than 20000. Theurethane polyol having a molecular weight of not greater than 20000 cancontribute to the stain resistance of the paint layer 6. From thisviewpoint, this molecular weight is more preferably not greater than18000 and particularly preferably not greater than 16000.

The urethane polyol has a hydroxyl value of preferably not less than 10mg KOH/g, more preferably not less than 15 mg KOH/g, and particularlypreferably not less than 20 mg KOH/g. The hydroxyl value is preferablynot greater than 200 mg KOH/g, more preferably not greater than 190 mgKOH/g, and particularly preferably not greater than 180 mg KOH/g. Thehydroxyl value is measured according to the standards of “JIS K 1557-1”.For the measurement, the acetylation method is adopted.

The polyisocyanate composition that is a curing agent liquid in thepaint contains a polyisocyanate compound. The polyisocyanate compoundhas two or more isocyanate groups.

Examples of the polyisocyanate compound include: aromatic diisocyanatessuch as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture(TDI) of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate,4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate(XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylenediisocyanate (PPDI); alicyclic or aliphatic diisocyanates such as4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophoronediisocyanate (IPDI), and norbornene diisocyanate (NBDI); andtriisocyanates such as an allophanate product, a biuret product, anisocyanurate product, an adduct product of diisocyanates. Thepolyisocyanate compound may include two or more isocyanates.

Examples of preferable triisocyanates include an isocyanurate product ofhexamethylene diisocyanate, a biuret product of hexamethylenediisocyanate, and an isocyanurate product of isophorone diisocyanate.

Preferably, the polyisocyanate composition contains a triisocyanatecompound. The proportion of the triisocyanate compound to the entirepolyisocyanate in the polyisocyanate composition is preferably not lessthan 50% by weight, more preferably not less than 60% by weight, andparticularly preferably not less than 70% by weight. The polyisocyanatecomposition may contain only the triisocyanate compound as thepolyisocyanate compound.

The isocyanate group amount (NCO %) of the polyisocyanate contained inthe polyisocyanate composition is preferably not less than 0.5% byweight, more preferably not less than 1.0% by weight, and particularlypreferably not less than 2.0% by weight. The isocyanate group amount ispreferably not greater than 45% by weight, more preferably not greaterthan 40% by weight, and particularly preferably not greater than 35% byweight. The isocyanate group amount (NCO %) is calculated by thefollowing mathematical formula.NCO=(100×Mi×42)/Wi

Mi: the number of moles of the isocyanate groups in the polyisocyanate

42: the molecular weight of NCO

Wi: the total weight (g) of the polyisocyanate

Specific examples of the polyisocyanate include: trade names “BURNOCKD-800”, “BURNOCK DN-950”, “BURNOCK DN-955”, manufactured by DICcorporation; trade names “Desmodur N 75 MPA/X”, “Desmodur N 3300”,“Desmodur L 75 (C)”, “Desmodur Z 4470”, and “Sumidur E21-1”,manufactured by Sumika Bayer Urethane CO., Ltd.; trade names “CORONATEHX” and “CORONATE HK”, manufactured by Tosoh Corporation; trade names“DURANATE 24A-100”, “DURANATE 21S-75E”, “DURANATE TPA-100”, and“DURANATE TKA-100”, manufactured by Asahi Kasei Chemicals Corporation;and trade name “VESTANAT T1890” manufactured by Degussa AG.

The mole ratio (NCO group/OH group) of the hydroxyl group (OH group) ofthe base material and the isocyanate group (NCO group) of the curingagent in the curing type paint composition is preferably not less than0.1. The paint layer 6 having excellent stain resistance can be formedfrom the composition in which the mole ratio (NCO group/OH group) is notless than 0.1. From this viewpoint, the mole ratio is particularlypreferably not less than 0.2. The mole ratio is preferably not greaterthan 2.0. The composition in which the mole ratio is not greater than2.0 can contribute to the spin performance of the golf ball 2. From thisviewpoint, the ratio is more preferably not greater than 1.8 andparticularly preferably not greater than 1.6.

The paint layer 6 can be formed by applying the paint onto the surfaceof the main body 4. The paint may be applied in an overlapped manner. Inthe case of application in an overlapped manner, the paint appliedearlier and the paint applied later may be of the same type or may be ofdifferent types.

The paint layer 6 preferably has a thickness Tp of not less than 5 μmand not greater than 50 μm. The paint layer 6 having a thickness Tp ofnot less than 5 μm can contribute to spin performance. From thisviewpoint, the thickness Tp is more preferably not less than 6 μm andparticularly preferably not less than 7 μm. The paint layer 6 having athickness Tp of not greater than 50 μm has excellent durability. Fromthis viewpoint, the thickness Tp is more preferably not greater than 40μm and particularly preferably not greater than 30 μm. In the case wherethe paint is applied in an overlapped manner, the total thickness of aplurality of layers only needs to fall within the above range.

The paint layer 6 preferably has an indentation depth of not less than300 nm and not greater than 3000 nm. The paint layer 6 having anindentation depth of not less than 300 nm can contribute to spinperformance. From this viewpoint, the indentation depth is morepreferably not less than 400 nm and particularly preferably not lessthan 500 nm. The paint layer 6 having an indentation depth of notgreater than 3000 nm has excellent stain resistance. From thisviewpoint, the indentation depth is more preferably not greater than2500 nm and particularly preferably not greater than 2000 nm.

In measurement of the indentation depth, the golf ball 2 is divided toobtain a hemisphere. On the hemisphere, a cross-section passing throughthe central point of the golf ball 2 is exposed. The cross-sectionincludes a cross-section of the paint layer 6. The cross-section of thehemisphere is made horizontal by a cryo-microtome. A penetrator of ananoindenter is brought into contact with the paint layer 6 in thiscross-section and pressed against the paint layer 6 in a directionperpendicular to the cross-section. Due to this pressing, the penetratoradvances. A load and an advancing distance of the penetrator aremeasured. The conditions at the measurement are as follows.

-   -   Nanoindenter: “ENT-2100” manufactured by ELIONIX INC.    -   Temperature: 30° C.    -   Penetrator: a Berkovich penetrator (65.03° As (h)=26.43 h²)    -   Number of partitions: 500 steps    -   Step interval: 20 msec (100 mgf)        The load of the penetrator is gradually increased until reaching        50 mgf. The advancing distance of the penetrator is measured        when the load is 30 mgf.

By the measurement of the indentation depth, the hardness of the paintlayer 6 can be evaluated without influence of the hardness of the cover12. The evaluation method according to the present invention includesthe steps of:

-   -   (1) cutting the golf ball 2 including the paint layer 6; and    -   (2) pressing a cross-section of the paint layer 6 exposed as a        result of the above cutting and measuring an indentation depth        of the paint layer 6.

Second Embodiment

A golf ball 20 shown in FIG. 2 includes a main body 22 and a paint layer24 positioned outside the main body 22. The main body 22 includes aspherical core 26 and a cover 28 positioned outside the core 26. Thegolf ball 20 has a so-called two-piece structure. The golf ball 20 has aplurality of dimples 30 on the surface thereof. Of the surface of thegolf ball 20, a part other than the dimples 30 is a land 32. The golfball 20 may include a mark layer. The mark layer may be positionedbetween the cover 28 and the paint layer 24, or may be positionedoutside the paint layer 24.

The golf ball 20 preferably has a diameter of not less than 40 mm andnot greater than 45 mm. From the viewpoint of conformity to the rulesestablished by the United States Golf Association (USGA), the diameteris particularly preferably not less than 42.67 mm. In light ofsuppression of air resistance, the diameter is more preferably notgreater than 44 mm and particularly preferably not greater than 42.80mm. The golf ball 20 preferably has a weight of not less than 40 g andnot greater than 50 g. In light of attainment of great inertia, theweight is more preferably not less than 44 g and particularly preferablynot less than 45.00 g. From the viewpoint of conformity to the rulesestablished by the USGA, the weight is particularly preferably notgreater than 45.93 g.

The core 26 is formed by crosslinking a rubber composition. For the core26, a rubber composition that is the same as the rubber composition ofthe core 8 shown in FIG. 1 can be used.

The core 26 has a diameter of preferably not less than 30.0 mm andparticularly preferably not less than 38.0 mm. The diameter of the core26 is preferably not greater than 42.0 mm and particularly preferablynot greater than 41.5 mm. The core 26 may include two or more layers.The core 26 may have a rib on the surface thereof. The core 26 may behollow.

The cover 28 is formed from a resin composition. For the cover 28, aresin composition that is the same as the resin composition of the midlayer 10 shown in FIG. 1 can be used. A preferable base polymer of theresin composition is an ionomer resin.

Instead of an ionomer resin or together with an ionomer resin, the resincomposition of the cover 28 may include another polymer. Examples of theother polymer include polystyrenes, polyamides, polyesters, polyolefins,and polyurethanes. The resin composition may include two or morepolymers.

The cover 28 preferably has a hardness Hc of not less than 50 and notgreater than 80. The cover 28 having a hardness Hc of not less than 50has excellent resilience performance. From this viewpoint, the hardnessHc is more preferably not less than 52 and particularly preferably notless than 54. The golf ball 20 including the cover 28 having a hardnessHc of not greater than 80 has excellent feel at impact and excellentspin performance. From this viewpoint, the hardness Hc is morepreferably not greater than 78 and particularly preferably not greaterthan 76.

The hardness Hc of the cover 28 is measured according to the standardsof “ASTM-D 2240-68”. The hardness Hc is measured with a Shore D typehardness scale mounted to an automated hardness meter (trade name “digitest II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). For themeasurement, a sheet that is formed by hot press, is formed from thesame material as that of the cover 28, and has a thickness of about 2 mmis used. Prior to the measurement, a sheet is kept at 23° C. for twoweeks. At the measurement, three sheets are stacked.

In light of durability, the cover 28 has a thickness Tc of preferablynot less than 0.5 mm, more preferably not less than 0.8 mm, andparticularly preferably not less than 1.0 mm. In light of feel atimpact, the thickness Tc is preferably not greater than 3.0 mm, morepreferably not greater than 2.7 mm, and particularly preferably notgreater than 2.5 mm. The thickness Tc is measured at a positionimmediately below the land 32.

The paint layer 24 is laminated on the cover 28. The paint layer 24 isformed from a resin composition. Examples of the base material of theresin composition include polyurethanes, epoxy resins, acrylic resins,polyvinyl acetate resins, and polyesters. Particularly preferable baseresins are polyurethanes. Polyurethanes can contribute to the spinperformance of the golf ball 20. For the paint layer 24, a resincomposition that is the same as the resin composition of the paint layer6 shown in FIG. 1 can be used.

The paint layer 24 can be formed by applying the paint onto the surfaceof the main body 22. The paint may be applied in an overlapped manner.In the case of application in an overlapped manner, the paint appliedearlier and the paint applied later may be of the same type or may be ofdifferent types.

The paint layer 24 preferably has a thickness Tp of not less than 5 μmand not greater than 50 μm. The paint layer 24 having a thickness Tp ofnot less than 5 μm can contribute to spin performance. From thisviewpoint, the thickness Tp is more preferably not less than 6 μm andparticularly preferably not less than 7 μm. The paint layer 24 having athickness Tp of not greater than 50 μm has excellent durability. Fromthis viewpoint, the thickness Tp is more preferably not greater than 40μm and particularly preferably not greater than 30 μm. In the case wherethe paint is applied in an overlapped manner, the total thickness of aplurality of layers only needs to fall within the above range.

The paint layer 24 preferably has an indentation depth of not less than300 nm and not greater than 3000 nm. The paint layer 24 having anindentation depth of not less than 300 nm can contribute to spinperformance. From this viewpoint, the indentation depth is morepreferably not less than 400 nm and particularly preferably not lessthan 450 nm. The paint layer 24 having an indentation depth of notgreater than 3000 nm has excellent stain resistance. From thisviewpoint, the indentation depth is more preferably not greater than2800 nm and particularly preferably not greater than 2500 nm.

[Preferable Combination of Hardness of Cover and Indentation Depth]

A combination of a cover having a hardness Hc of not less than 20 andnot greater than 50 and a paint layer having an indentation depth of notless than 400 nm and not greater than 3000 nm is preferable. Acombination of a cover having a hardness Hc of not less than 50 and notgreater than 80 and a paint layer having an indentation depth of notless than 300 nm and not greater than 2500 nm is also preferable.

EXAMPLES Example 1

A rubber composition was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (trade name “BR-730”, manufactured by JSRCorporation), 23.5 parts by weight of zinc diacrylate, 5 parts by weightof zinc oxide, an appropriate amount of barium sulfate, and 0.95 partsby weight of dicumyl peroxide. This rubber composition was placed into amold including upper and lower mold halves each having a hemisphericalcavity, and heated at 155° C. for 18 minutes to obtain a core with adiameter of 38.7 mm. The amount of barium sulfate was adjusted such thata core having a predetermined weight was obtained.

A resin composition was obtained by kneading 55 parts by weight of anionomer resin (trade name “Himilan AM7329”, manufactured by DuPont-MITSUI POLYCHEMICALS Co., Ltd.), 45 parts by weight of anotherionomer resin (trade name “Himilan 1555”, manufactured by Du Pont-MITSUIPOLYCHEMICALS Co., Ltd.), an appropriate amount of barium sulfate, and 3parts by weight of titanium dioxide with a twin-screw kneading extruder.The core was covered with this resin composition by injection molding toform a cover with a thickness of 2.0 mm.

Polytetramethylene ether glycol (PTMG, number average molecular weight:650) and trimethylol propane (TMP) were dissolved in a solvent (tolueneand methyl ethyl ketone). The mole ratio (PTMG:TMP) was 1.8:1.0.Dibutyltin dilaurate was added to this solution as a catalyst in anamount of 0.1% by weight with respect to the entire base material. Whilethis polyol solution was kept at 80° C., isophorone diisocyanate (IPDI)was dropped and mixed into the polyol solution. The mole ratio (NCO/OH)of this mixture solution was 0.6. After the dropping, the mixturesolution was continuously agitated until isocyanate was eliminated.Thereafter, the mixture solution was cooled at normal temperature toobtain a base material that is a urethane polyol composition. Thedetails of this base material are as follows.

-   -   Solid content: 30% by weight    -   Content of PTMG: 67% by weight    -   Hydroxyl value of solid content: 67.4 mg KOH/g    -   Weight average molecular weight of urethane polyol: 4867

Mixed were 30 parts by weight of an isocyanurate-modified product ofhexamethylene diisocyanate (trade name “DURANATE TKA-100”, manufacturedby Asahi Kasei Chemicals Corporation, NCO content: 21.7% by weight), 30parts by weight of a biuret-modified product of hexamethylenediisocyanate (trade name “DURANATE 21S-75E”, manufactured by Asahi KaseiChemicals Corporation, NCO content: 15.5% by weight), and 40 parts byweight of an isocyanurate-modified product of isophorone diisocyanate(trade name “Desmodur Z 4470”, manufactured by Sumika Bayer UrethaneCO., Ltd., NCO content: 11.9% by weight). A mixed solvent of methylethyl ketone, n-butyl acetate, and toluene was added as a solvent tothis mixture to obtain a curing agent that is a polyisocyanatecomposition. The concentration of the polyisocyanate component in thiscuring agent was 60% by weight.

A paint was obtained by mixing the aforementioned base material(urethane polyol composition) and the aforementioned curing agent(polyisocyanate composition). The mixing ratio (weight ratio) of thebase material and the curing agent was 6.4/1. The surface of a main bodyconsisting of the aforementioned core and the aforementioned cover wastreated with sandblast, and the paint was applied to the cover. Thepaint was dried at 40° C. for 24 hours to obtain a golf ball including apaint layer. The diameter of the golf ball was about 42.7 mm, and theweight of the golf ball was about 45.6 g.

Examples 2 and 3 and Comparative Examples 1 and 2

Golf balls of Examples 2 and 3 and Comparative Examples 1 and 2 wereobtained in the same manner as Example 1, except the mixing ratio of theurethane polyol composition and the polyisocyanate composition was asshown in Tables 3 and 4 below.

Examples 4 and 5

Golf balls of Examples 4 and 5 were obtained in the same manner asExample 1, except the composition of the cover was as shown in Table 4below. The composition of the cover is shown in detail in Table 2 below.

Example 6

A rubber composition was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (trade name “BR-730”, manufactured by JSRCorporation), 30.5 parts by weight of zinc diacrylate, 10 parts byweight of zinc oxide, an appropriate amount of barium sulfate, 0.1 partsby weight of 2-thionaphthol, 0.3 parts by weight of pentabromo diphenyldisulfide, 0.7 parts by weight of dicumyl peroxide, and 2 parts byweight of benzoic acid. This rubber composition was placed into a moldincluding upper and lower mold halves each having a hemisphericalcavity, and heated at 150° C. for 19 minutes to obtain a core with adiameter of 39.7 mm. The amount of barium sulfate was adjusted such thata core having a predetermined weight was obtained.

A resin composition was obtained by kneading 55 parts by weight of anionomer resin (trade name “Himilan AM7329”, manufactured by DuPont-MITSUI POLYCHEMICALS Co., Ltd.), 45 parts by weight of anotherionomer resin (trade name “Himilan 1555”, manufactured by Du Pont-MITSUIPOLYCHEMICALS Co., Ltd.), an appropriate amount of barium sulfate, and 3parts by weight of titanium dioxide with a twin-screw kneading extruder.The core was covered with this resin composition by injection molding toform a mid layer with a thickness of 1.0 mm.

A paint composition (trade name “POLIN 750LE”, manufactured by SHINTOPAINT CO., LTD.) including a two-component curing type epoxy resin as abase polymer was prepared. The base material liquid of this paintcomposition includes 30 parts by weight of a bisphenol A type epoxyresin and 70 parts by weight of a solvent. The curing agent liquid ofthis paint composition includes 40 parts by weight of a modifiedpolyamide amine, 55 parts by weight of a solvent, and 5 parts by weightof titanium dioxide. The weight ratio of the base material liquid to thecuring agent liquid is 1/1. This paint composition was applied to thesurface of the mid layer with a spray gun, and kept at 23° C. for 12hours to obtain a reinforcing layer with a thickness of 10 μm.

A resin composition was obtained by kneading 100 parts by weight of athermoplastic polyurethane elastomer (trade name “Elastollan NY80A”,manufactured by BASF Japan Ltd.), 4 parts by weight titanium dioxide,and 0.04 parts by weight of ultramarine blue with a twin-screw kneadingextruder. Half shells were obtained from this resin composition bycompression molding. The sphere consisting of the core, the mid layer,and the reinforcing layer was covered with two of these half shells.These half shells and the sphere were placed into a final mold thatincludes upper and lower mold halves each having a hemispherical cavityand having a large number of pimples on its cavity face, and a cover wasobtained by compression molding. The thickness of the cover was 0.5 mm.

Polytetramethylene ether glycol (PTMG, number average molecular weight:650) and trimethylol propane (TMP) were dissolved in a solvent (tolueneand methyl ethyl ketone). The mole ratio (PTMG:TMP) was 1.8:1.0.Dibutyltin dilaurate was added to this solution as a catalyst in anamount of 0.1% by weight with respect to the entire base material. Whilethis polyol solution was kept at 80° C., isophorone diisocyanate (IPDI)was dropped and mixed into the polyol solution. The mole ratio (NCO/OH)of this mixture solution was 0.6. After the dropping, the mixturesolution was continuously agitated until isocyanate was eliminated.Thereafter, the mixture solution was cooled at normal temperature toobtain a base material that is a urethane polyol composition. Thedetails of this composition are as follows.

-   -   Solid content: 30% by weight    -   Content of PTMG: 67% by weight    -   Hydroxyl value of solid content: 67.4 mg KOH/g    -   Weight average molecular weight of urethane polyol: 4867

Mixed were 30 parts by weight of an isocyanurate-modified product ofhexamethylene diisocyanate (trade name “DURANATE TKA-100”, manufacturedby Asahi Kasei Chemicals Corporation, NCO content: 21.7% by weight), 30parts by weight of a biuret-modified product of hexamethylenediisocyanate (trade name “DURANATE 21S-75E”, manufactured by Asahi KaseiChemicals Corporation, NCO content: 15.5% by weight), and 40 parts byweight of an isocyanurate-modified product of isophorone diisocyanate(trade name “Desmodur Z 4470”, manufactured by Sumika Bayer UrethaneCO., Ltd., NCO content: 11.9% by weight). A mixed solvent of methylethyl ketone, n-butyl acetate, and toluene was added as a solvent tothis mixture to obtain a polyisocyanate composition that is a curingagent. The concentration of the polyisocyanate component in thiscomposition was 60% by weight.

A paint was obtained by mixing the aforementioned base material(urethane polyol composition) and the aforementioned curing agent(polyisocyanate composition). The mixing ratio (weight ratio) of thebase material and the curing agent on the solid content basis was 6.4/1.The surface of a main body consisting of the aforementioned core, theaforementioned mid layer, the aforementioned reinforcing layer, and theaforementioned cover was treated with sandblast, and the paint wasapplied to the cover. The paint was dried at 40° C. for 24 hours toobtain a golf ball including a paint layer. The diameter of the golfball was about 42.7 mm, and the weight of the golf ball was about 45.6g.

Examples 7 and 8 and Comparative Examples 3 and 4

Golf balls of Examples 7 and 8 and Comparative Examples 3 and 4 wereobtained in the same manner as Example 6, except the mixing ratio of theurethane polyol composition and the polyisocyanate composition was asshown in Tables 5 and 6 below.

Example 9

A golf ball of Example 9 was obtained in the same manner as Example 6,except the composition of the cover was as shown in Table 6 below. Thecomposition of the cover is shown in detail in Table 2 below.

[Amount of Compressive Deformation]

The amount of compressive deformation of a golf ball was measured with aYAMADA type compression tester. In the tester, the golf ball was placedon a hard plate made of metal. Next, a cylinder made of metal graduallydescended toward the golf ball. The golf ball, squeezed between thebottom face of the cylinder and the hard plate, became deformed. Amigration distance of the cylinder, starting from the state in which aninitial load of 98 N was applied to the golf ball up to the state inwhich a final load of 1274 N was applied thereto, was measured. A movingspeed of the cylinder until the initial load was applied was 0.83 mm/s.A moving speed of the cylinder after the initial load was applied untilthe final load was applied was 1.67 mm/s.

[Spin Rate]

A sand wedge was attached to a swing machine manufactured by GolfLaboratories, Inc. A golf ball was hit under a condition of a head speedof 16 m/sec, and the rate of backspin was measured. The average value ofdata obtained by 10 measurements is shown in Tables 3 to 6 below.

[Feel at Impact]

Thirty golf players hit golf balls with wedges and were asked about feelat impact. The evaluation was categorized as follows on the basis of thenumber of golf players who answered, “the feel at impact was good”.

-   -   A: 25 persons or more    -   B: 20 to 24 persons    -   C: 15 to 19 persons    -   D: 14 persons or less        The results are shown in Tables 3 to 6 below.

[Stain Resistance]

The color tone (L, a, b) of the surface of a golf ball was measured witha color difference meter (“CM3500D” manufactured by KONICA MINOLTA,INC.). An ethanol solution including 6% by weight of iodine and 4% byweight of potassium iodide (that is, iodine tincture) was prepared. Theiodine tincture was diluted with water to 40-fold. The golf ball wasimmersed in the diluted solution for 30 seconds. The diluted solutionadhering to the surface of the golf ball taken out from the dilutedsolution was wiped off. The color tone of the golf ball was measuredagain. A color difference ΔE was calculated on the basis of thefollowing mathematical formula.ΔE=(ΔL ² +Δa ² +Δb ²)^(1/2)The evaluation was categorized as follows on the basis of the colordifference ΔE.

-   -   A: ΔE is equal to or less than 15.    -   B: ΔE exceeds 15 and is equal to or less than 20.    -   C: ΔE exceeds 20 and is equal to or less than 25.    -   D: ΔE exceeds 25        The results are shown in Tables 3 to 6 below.

TABLE 1 Composition of Core (parts by weight) I II Polybutadiene rubber100 100 Zinc diacrylate 23.5 30.5 Zinc oxide 5 10 Barium sulfate * *2-thionaphthol — 0.1 Pentabromo diphenyl disulfide — 0.3 Diphenyldisulfide — — Dicumyl peroxide 0.95 0.7 Benzoic acid — 2 CrosslinkingTemp. (° C.) 155 150 Crosslinking time (min) 18 19 Compressivedeformation (mm) 3.5 3.3 Central hardness Ho(ShoreC) 64 53 Surfacehardness Hs(ShoreC) 80 80 Hs − Ho 16 27 * Appropriate amount

TABLE 2 Compositions of Mid Layer and Cover (parts by weight) a b c d eSurlyn 8150 — — 32.5 — — Surlyn 9150 — — 32.5 — — Polyamide 6 — — 35 — —Himilan AM7337 26 — — — — Himilan AM7329 26 55 — — — Himilan 1555 — 45 —— — RABALON T3221C 48 — — — — Elastollan NY80A — — — 100 — ElastollanNY97A — — — — 100 Barium sulfate * * * — — Titanium dioxide  6  3 4 4 4Ultramarine blue — — — 0.04 0.04 Hardness(ShoreD) 35 62 72 27 47 *Appropriate amount

TABLE 3 Results of Evaluation Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 3 CoreComposition I I I I Diameter (mm) 38.7 38.7 38.7 38.7 Ho (Shore C) 64 6464 64 Hs (Shore C) 80 80 80 80 Hs − Ho 16 16 16 16 Mid Composition — — —— layer Hardness — — — — (Shore D) Thickness(mm) — — — — CoverComposition b b b b Hardness 62 62 62 62 (Shore D) Thickness(mm) 2.0 2.02.0 2.0 Paint Mixing ratio 2.6/1 3.06/1 6.4/1 6.8/1 layer Indentation290 390 1250 1500 depth (nm) Thickness (μm) 10 10 10 10 Compressive 2.82.8 2.8 2.8 deformation (mm) Spin rate (rpm) 3650 3800 3950 4000 Feel atimpact C B A A Stain resistance A A B B

TABLE 4 Results of Evaluation Comp. Ex. 2 Ex. 4 Ex. 5 Core Composition II I Diameter (mm) 38.7 38.7 38.7 Ho (Shore C) 64 64 64 Hs (Shore C) 8080 80 Hs − Ho 16 16 16 Mid Composition — — — layer Hardness — — — (ShoreD) Thickness(mm) — — — Cover Composition b a c Hardness 62 35 72 (ShoreD) Thickness (mm) 2.0 2.0 2.0 Paint Mixing ratio 20/1 6.4/1 6.4/1 layerIndentation 3400 1250 1250 depth (nm) Thickness (μm) 10 10 10Compressive 2.8 2.9 2.7 deformation (mm) Spin rate (rpm) 4200 4100 3600Feel at impact A A B Stain resistance D B B

TABLE 5 Results of Evaluation Comp. Ex. 3 Ex. 7 Ex. 6 Core CompositionII II II Diameter (mm) 39.7 39.7 39.7 Ho (Shore C) 53 53 53 Hs (Shore C)80 80 80 Hs − Ho 27 27 27 Mid Composition b b b layer Hardness 62 62 62(Shore D) Thickness (mm) 1.0 1.0 1.0 Cover Composition d d d Hardness 2727 27 (Shore D) Thickness (mm) 0.5 0.5 0.5 Paint Mixing ratio 2.6/13.06/1 6.4/1 layer Indentation 290 390 1250 depth (nm) Thickness (μm) 1010 10 Compressive 2.9 2.9 2.9 deformation (mm) Spin rate (rpm) 4300 44504600 Feel at impact C B A Stain resistance A A B

TABLE 6 Results of Evaluation Comp. Ex. 8 Ex. 4 Ex. 9 Core CompositionII II II Diameter (mm) 39.7 39.7 39.7 Ho (Shore C) 53 53 53 Hs (Shore C)80 80 80 Hs − Ho 27 27 27 Mid Composition b b b layer Hardness 62 62 62(Shore D) Thickness (mm) 1.0 1.0 1.0 Cover Composition d d e Hardness 2727 47 (Shore D) Thickness (mm) 0.5 0.5 0.5 Paint Mixing ratio 6.8/1 20/16.4/1 layer Indentation 1500 3400 1250 depth (nm) Thickness (μm) 10 1010 Compressive 2.9 2.9 2.9 deformation (mm) Spin rate (rpm) 4650 48004200 Feel at impact A A B Stain resistance B D B

As shown in Tables 3 to 6, the golf ball of each Example is excellent invarious performance characteristics. From the results of evaluation,advantages of the present invention are clear.

The paint layer described above is applicable to a one-piece ball, afour-piece ball, a five-piece ball, a six-piece ball, a thread-woundball, and the like in addition to a two-piece ball and a three-pieceball. The golf ball according to the present invention is suitable for,for example, playing golf on golf courses and practicing at drivingranges. The above descriptions are merely illustrative examples, andvarious modifications can be made without departing from the principlesof the present invention.

The invention claimed is:
 1. A golf ball comprising a main body and apaint layer positioned outside the main body, wherein the main bodyconsists of a core and a cover positioned outside the core, the paintlayer is laminated on the cover, the paint layer has a thickness of 40μm or less, when the paint layer is pressed in a direction perpendicularto a cross-section along a plane passing through a central point of thegolf ball, the measured paint layer indentation depth is not less than300 nm and not greater than 1500 nm, the cover has a Shore D hardness ofnot less than 54 and not greater than 80, and the cover has a thicknessof not less than 1.0 mm and not greater than 3.0 mm.
 2. The golf ballaccording to claim 1, wherein the measured indentation depth is not lessthan 400 nm and not greater than 1500 nm.
 3. The golf ball according toclaim 1, wherein the paint layer is formed from a polyurethane paint. 4.The golf ball according to claim 3, wherein the polyurethane paintcontains a polyol composition which contains a urethane polyol.
 5. Thegolf ball according to claim 4, wherein the urethane polyol is formedfrom a polyisocyanate component and a polyether diol component which hasa number average molecular weight of not less than 550 and not greaterthan 3,000.
 6. The golf ball according to claim 5, wherein the contentof the polyether diol component in the urethane polyol is not less than60% by weight.
 7. The golf ball according to claim 1, wherein the paintlayer is formed from a polyurethane paint which contains apolyisocyanate composition which contains a triisocyanate compound, andthe proportion of triisocyanate compound to all polyisocyanatecomponents in the polyisocyanate composition is not less than 50% byweight.
 8. The golf ball according to claim 1, wherein the cover has aShore D hardness of not less than 54 and not greater than 76, and athickness of not less than 1.0 mm and not greater than 2.7 mm.
 9. Thegolf ball according to claim 6, wherein the cover has a Shore D hardnessof not less than 54 and not greater than 76, and a thickness of not lessthan 1.0 mm and not greater than 2.7 mm.